The present invention generally relates to compounds that act as to prevent or diminish polymer combustion. In particular, the present invention relates to synthesizing non-halogenated aromatic flame retardants and blending them into polymer-containing materials, giving the polymer-containing materials practical flame retardance.
Each year in the United States, fires lead to numerous losses of life and property. Annual property losses are currently estimated at over $8 billion, while fires are responsible for approximately 29,000 injuries and 4,500 deaths annually. Structural fires are especially common, and the majority of the combustible materials in fatal fires are polymer-containing materials. In an effort to prevent such fire-related tragedies, flame retardants are commonly added to plastics and other polymeric materials used in buildings, aircraft, and various transportation vehicles.
In order to effectively treat polymer-containing materials for flame retardance, the manner in which polymers burn must first be investigated. The exact mechanism for polymer combustion is not known, although some information is known regarding fire propagation within polymers. The heat generated from a flame breaks down or decomposes the polymer, resulting in depolymerization and volatilization of the monomers in the pyrolysis zone. These volatile monomers or fragments diffuse into the flame zone and undergo oxidative degradation by reacting with oxygen according to a free-radical chain process. This reactivity causes the production and release of additional heat that further breaks down the polymer. If the polymer is further degraded, more fuel is produced, and the fire is therefore continuously fed. Thus, the process of polymer combustion is cyclic, and flame retardance for polymers is only achieved when this cycle of degradation and refueling is broken. Hence, methods for adding flame retardance to polymer-containing materials must interfere with this degradation cycle.
There are predominantly three methods currently being employed for adding flame retardance to polymer-containing materials. In the first method, xe2x80x9chigh-charxe2x80x9d forming materials are used. Char is a carbon-based soot or residue that undergoes very little oxidative degradation and prevents the passage of fuel molecules to the flame. Such xe2x80x9chigh-charxe2x80x9d materials form an insulating outer layer of carbon or ceramic that prevents flammable gases resulting from the plastic decomposition from reaching the vapor phase (the phase in which combustion occurs). Also, thick char does not allow heat to reach the remaining underlying polymers; thus, the char is able to prevent melt, flow, and thermal decomposition of the polymer-containing materials. Examples of xe2x80x9chigh-charxe2x80x9d forming materials used in these applications include cross-linking agents, phosphorous-containing compounds, and the like. Cross-linking agents aid in flame retardance because a cross-linked polymeric network is formed, the flow of molten polymer is restricted and is unable to continue propagation of the flame.
Another method used to prevent the combustion of polymer-containing compounds involves the use of materials that, upon heating, either endothermically cool or release non-flammable gases. Materials that are commonly used for such applications include hydrated alumina (which releases water upon heating), sodium bicarbonate (which releases non-flammable carbon dioxide upon heating), and the like.
A third method of adding flame retardance to polymer-containing materials involves the slowing or retardation of the combustion process in the vapor phase of the fire. This is usually accomplished through the use of halogenated materials. Such halogenated materials may include brominated additives that employ bromine as a flame-front poison. Thus, the bromine derivatives work in the vapor phase of the burning polymers in order to prevent flame propagation.
A need currently exists for developing a way of using non-halogenated compounds as effective flame retardants for plastics and polymer-containing materials. A need also exists for compounds to be used as effective flame retardants even when a constant flame is present. The process for using such compounds is therefore disclosed in the present invention.
The present invention utilizes non-halogenated aromatic compounds as flame retardants for polymer containing materials. Specifically, the compounds may be various non-halogenated aromatics such as the aromatic boronic acids. Suitable aromatic compounds include 1,4-benzenediboronic acid, although other non-halogenated compounds may be utilized. Various polymer-containing materials may utilize the flame retardants of the present invention. Examples include the polycarbonates, acrylonitrile-butadiene-styrenes, and high impact polystyrenes, as well as polyethylenes and polypropylenes.